The invention relates to a pump for delivering corrosive media of a high temperature and to a method for operating this pump. Pumps for delivering hazardous media are known. Magnetically coupled pumps are in most cases used for this purpose in order to avoid problems concerning tightness at drive shaft bushes, which are usually inevitable. In this case the actual delivery medium is used to lubricate the bearing, which is usually disposed in the vicinity of the internally operating magnets, and therefore fills the entire pump interior. Various materials may be used for the entire pump interior where corrosive media are concerned. It is also known to seal off the pump chamber from the pump interior by, for example, axial ring seals and to separately lubricate the shaft bearings lying in the vicinity of the inner magnets, for example by means of a side stream of the delivery medium. The disadvantage of these pumps lies in the fact that they cannot deliver highly corrosive media. Added to this problem is the fact that the highly corrosive media which are to be delivered have a high temperature (&gt;300.degree. C.), as is the case of, for example, salt melts, and no sealing material satisfies these two requirements regarding resistance to heat and corrosion. Moreover, the inner pump magnets increasingly lose their magnetism at higher temperatures, this gradually disappearing at temperatures above 400.degree. C. in the case of currently known magnetic materials, so that the pump becomes unserviceable.
There is known in the prior art a pump unit for delivering hot media which has a cooling flow guide such that the cooling air flow of the electric motor driving the pump is directed towards the bearing supports and the magnetic coupling. The operating temperature of the magnets and the bearings is as a result lowered in a way which simplifies construction, even when delivering hot media, and the pump remains in working order. However a pump of this kind is not suitable for delivering hot, highly corrosive media, such as salt melts, as a large number of parts which are contacted by the media and which would very quickly be corroded by the salt melt are disposed in the interior.
DE-A 4 212 982 proposes a magnetically coupled pump for delivering hot media. The object of this invention is also to cool bearings and magnets when delivering hot media so as to confine the bearing and magnet temperatures. This object is solved in that a coolant inflow channel is provided in the drive shaft for the outer magnet support, which channel communicates with a coolant gap which in turn communicates with the outer magnet support and the inside of an outer pump enclosure, the cooling fluid being evacuated from the outer enclosure again. Media of temperatures between 200.degree. and 300.degree. C. can be delivered by a pump according to this solution, in which case the bearing temperatures should not exceed 50.degree. to 60.degree. C. However the proposed pump cannot fulfil the requirement of guaranteeing a reliable seal against a highly corrosive medium which is to be delivered directly in its bearings lying closest to the pump casing, this being impossible to achieve with known sealing materials which are necessary in the construction which is presented. Moreover, the cooling of the inner bearings which is provided would cause crystallisation of the salt melt in the bearing, resulting directly in its destruction not just through corrosion, but also through erosion. The proposed solution cannot prevent salt melt from passing out of the pump casing through the inner bearings and into the pump interior, as no suitable sealing materials are available. However a process of this kind very quickly destroys the pump.
The object is therefore to find a pump and a method for operating this pump which permit the delivery of highly corrosive and high-temperature media such as, e.g. chloride or Cu salt melts of temperatures exceeding 400.degree. C., with the pump being of a simple structure, reliable and inexpensive to operate.